[Combined Documentation] Targets are missing some dependencies

Creating this issue that was brought to my attention by @nmggithub:

The new experimental combined documentation support doesn't provide targets with all of their dependencies' documentation.

Checklist

[x] If possible, I've reproduced the issue using the main branch of this package.
[x] This issue hasn't been addressed in an existing GitHub issue.

Expected behavior

A target with multiple dependencies should be able to link against all of those dependencies

Actual behavior

A target with multiple dependencies is only able to link against one of its dependencies

Steps to Reproduce

Build combined documentation for a package where one of the targets depends on two or more other targets in that package, passing the --verbose flag.

In the docc convert call for the target with two or more dependencies there should be as many --dependency arguments.

Swift-DocC Plugin Version Information

Swift-DocC plugin version: 1.4.2 for example, or a commit hash. Swift Compiler version: swiftlang-6.0.0.9.10 clang-1600.0.26.2 (but it's not relevant to this bug)

swiftlang / swift-docc-plugin